ERAP-1 (endoplasmic-reticulum aminopeptidase-1) is a multifunctional enzyme with roles in the regulation of blood pressure, angiogenesis and the presentation of antigens to MHC class I molecules. Whereas the enzyme shows restricted specificity toward synthetic substrates, its substrate specificity toward natural peptides is rather broad. Because of the pathophysiological significance of ERAP-1, it is important to elucidate the molecular basis of its enzymatic action. In the present study we used site-directed mutagenesis to identify residues affecting the substrate specificity of human ERAP-1 and identified Gln(181) as important for enzymatic activity and substrate specificity. Replacement of Gln(181) by aspartic acid resulted in a significant change in substrate specificity, with Q181D ERAP-1 showing a preference for basic amino acids. In addition, Q181D ERAP-1 cleaved natural peptides possessing a basic amino acid at the N-terminal end more efficiently than did the wild-type enzyme, whereas its cleavage of peptides with a non-basic amino acid was significantly reduced. Another mutant enzyme, Q181E, also revealed some preference for peptides with a basic N-terminal amino acid, although it had little hydrolytic activity toward the synthetic peptides tested. Other mutant enzymes, including Q181N and Q181A ERAP-1s, revealed little enzymatic activity toward synthetic or peptide substrates. These results indicate that Gln(181) is critical for the enzymatic activity and substrate specificity of ERAP-1.

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Caveolin-1 is implicated in the regulation

Adult T-cell leukemia (ATL) is a T-cell malignancy etiologically associated with human T-cell leukemia virus type 1 (HTLV-1). Twist, a highly conserved basic helix-loop-helix transcription factor, is a newly identified oncogene. However, there are no reports on Twist expression in ATL. To define the role of Twist in leukemogenesis of ATL, we examined its expression in T-cell lines and PBMC. HTLV-1-infected T-cell lines and ATL cells expressed high levels of Twist compared with uninfected T-cell lines and normal PBMC. Immunohistochemistry showed immunostaining for Twist in ATL cells in ATL lymph nodes and skin lesions. Infection of normal PBMC with HTLV-1 induced Twist expression. Induction of the viral protein Tax in a human T-cell line led to upregulation of Twist. Tax-induced Twist expression involved the NF-kappaB and CREB signaling pathways. Twist augmented Tax-mediated HTLV-1 LTR and NF-kappaB activation. Short interfering RNA against Twist inhibited cell growth of HTLV-1-infected T-cell lines and downregulation of Twist expression in an HTLV-1-infected T-cell line inhibited the expression of Akt1, interleukin-2 receptor alpha chain, and Tax as well as the known target genes of Twist, YB-1 and Akt2. In conclusion, the results suggest that Tax-induced induction of Twist contributes to leukemogenesis of ATL.

Adult T-cell lymphoma/leukemia (ATLL) is a T-cell malignancy caused by the human T-lymphotrophic virus type I (HTLV-I), and its therapeutic outcome still remains extremely poor. Therefore, novel therapeutic strategies are needed to improve treatment outcomes. In this study, we elucidated the therapeutic potential of targeting the anti-apoptotic Bcl-2 family proteins for the treatment of ATLL using ABT-737 (Abbott Laboratories, Abbott Park, IL, USA), a small molecule inhibitor of Bcl-2, Bcl-XL and Bcl-w. We first validated the rationale of this study by immunohistochemically assessing the expression of Bcl-2 family proteins in 25 lymph-node specimens derived from ATLL patients. The Bcl-2 and/or Bcl-XL proteins were expressed in 80% of specimens. We next examined the cytotoxicity of ABT-737 against three ATLL cell lines by the Colorimetric method. ABT-737 significantly inhibited growth of MT-1, MT-2 and HuT 102 cells with concentrations of 50 percent inhibition of 2.4, 0.23 and 0.008μM at 72 h, respectively. We then tried to clarify the mechanism of growth inhibition induced with ABT-737 using MT-1 and MT-2 cells. ABT-737 induced apoptosis in both cells with cleavage of caspases 9 and 3, and PARP. ABT-737 also induced apoptosis in fresh tumor cells derived from patients with ATLL. We also tested if ABT-737 enhances the cytotoxicity induced by conventional chemotherapeutic agents or novel agents. The interactions between them were evaluated using the Chou-Talalay method. ABT-737 synergistically enhanced the cytotoxicity and apoptosis induced by doxorubicin, vincristine or etoposide and bortezomib or suberolyanilide hydroxamic acid, which are current key drugs and promising candidates for the treatment of ATLL, respectively. Finally, we investigated the growth inhibition of ABT-737 in ATLL-xenografted mice. The mean tumor volume and weight, and mean serum level of soluble interleukin-2 receptor α at day 21 of the treated mice with ABT-737 (100mg/kg/day) were significantly lower than those of vehicle-treated mice. Moreover, massive induction of apoptosis was observed in tumors treated with ABT-737 by the TUNEL assay. These results suggest that the use of ABT-737, either alone, or in combination with other conventional cytotoxic and novel drugs, represents a promising novel targeted approach to overcome drug resistance and to improve patient outcome in ATLL. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4524.